In manufacturing semiconductor devices, resist patterns have been required to be made minute enough to meet increased integration density and highly accelerated processing speed in LSIs. Resist patterns are normally formed in photo-lithographic processes from, for example, positive-working type resists, whose solubilities to alkali developers are increased by exposure to light. Accordingly, the resists in the areas exposed to light are removed with the alkali developers to form positive resist patterns. However, the fineness of the resultant patterns greatly depends on the exposure methods and light sources, and hence in order to stably produce fine resist patterns, a huge investment is necessary to install special and expensive facilities and equipments needed for the exposure methods and light sources capable of ensuring the fineness.
In view of that, there are various techniques studied for further miniaturizing resist patterns beforehand formed by conventional methods. For example, they include a practical method in which a resist pattern stably produced by a conventional method is coated with a composition comprising a water-soluble resin and optional additives (hereinafter, such composition is often referred to as “a fine pattern-forming composition”) so as to fatten or thicken the resist pattern and thereby to decrease the diameter of holes and/or the width of furrow lines separating the ridges in the pattern.
Specifically, the following processes and composition are known, that is:
(1) a process comprising the steps of
coating a conventionally formed resist pattern with a fine pattern-forming composition crosslinkable by an acid,
heating the resist pattern to diffuse the acid contained in the resist so that the composition on the resist may be crosslinked to form a crosslinked layer at the interface therebetween as a covering layer of the resist pattern, and
removing the uncrosslinked composition with a developer to fatten or thicken the resist pattern and thereby to decrease the diameter of holes and/or the width of furrow lines separating the ridges in the pattern (see, Patent documents 1 and 2);
(2) a process comprising the steps of
coating a conventionally formed resist pattern with a fine pattern-forming composition comprising a copolymer derived from (meth)acrylic acid monomers and water-soluble vinyl monomers, and
heating the resist pattern to shrink and thereby to become finer (see, Patent document 3); and
(3) a water-soluble fine pattern-forming composition which comprises a polymer containing amino groups, in particular, primary amines and which is used for covering a photoresist pattern (see, Patent document 4).
In each of the above processes, there are two casting procedures. One is the step of casting a resist composition on the substrate, and the other is the step of casting a fine pattern-forming composition on the resist pattern. Those two casting procedures are often carried out by means of the same coating apparatus so as to simplify the production facilities. Further, since resist patterns are usually produced in a clean room having limited space, it saves the space in the clean room to use the same coating apparatus.
However, the present inventors have found that there may be a problem if the same coating apparatus is used to cast the resist composition and the fine pattern-forming composition. Specifically, generally when a composition is cast with a coating apparatus, excess of the composition is discharged as a waste solution. In addition, also when excess of the composition is washed way with a detergent such as an edge-rinsing solution, the mixture of the composition and the detergent is discharged as another waste solution. Those waste solutions are drained out of the apparatus through pipes, and hence in general they partly adhere to and remain on the inside walls of the pipes unless the pipes are cleaned every time. Accordingly, if the same coating apparatus is used to cast the resist composition and the fine pattern-forming composition, they are inevitably brought in contact with each other in the pipes. At that time, solid precipitates are often deposited by conventional fine pattern-forming compositions. Since the precipitates may choke up the pipes to lower the productivity, it has been desired to improve this problem.